1. Field of the Invention
This invention relates, generally, to micro-fluidic control. More particularly, it relates to means for controlling flow in ultra low flow regimes involving small passages.
2. Description of the Prior Art
Conventional machining methods can make a flow passage having a diameter of 0.001 inch. Although technically possible, practically such small single holes become clogged easily by contamination.
One known technique is to provide a series of nested large passages to create the effect of a single, much smaller hole. More particularly, a series of flow chambers is patterned into a circular wafer form, also called a plate. Each flow chamber includes two opposing circular lobes connected by a long, narrow rectangular channel. This technique has utility in hydraulic systems where very low flow passages that are not contamination sensitive are required.
This prior art design employs parallel rectangular channel lines tangentially connecting diametrically opposed circular lobes. Entering fluid meets an abrupt pressure drop at an initial flow chamber where an initial lobe exits to a far more narrow entry to a rectangular interconnecting passage. For flow restrictors, an abrupt pressure drop can cause cavitation or pseudo-cavitation, i.e., an entrained air release. Either way, bubbles may release into fluid channels causing hydraulic action to become “spongy,” i.e., to have lessened hydraulic effectiveness. Hydraulics depends upon the use of incompressible fluid to transmit power. Accordingly, air mixed into hydraulic oil lessens hydraulic effectiveness by making the fluid more compressible.
Pressure spike attenuators, also known as snubbers, are designed to cancel pressure spikes upon entry into pressure transducers. Pressure spikes, whether created by a severe pump ripple or water hammer effects, are damaging to fluid system components such as pressure transducers that contain sensitive electronics.
What is needed, then, is an improved micro-fluidic control means that inhibits or eliminates bubble formation by reducing or eliminating abrupt pressure drops, thereby increasing hydraulic effectiveness.
There is a need as well for improvements in pressure spike attenuators and static mixers.
However, in view of the prior art taken as a whole at the time the present invention was made, it was not obvious to those of ordinary skill how the identified needs could be fulfilled.